Variable pitch propeller



Nov. 3, 1953 Filed Aug. 28, 1947 M. E. CUSHMAN VARIABLE PITCH PROPE LLER 5 Sheets-Sheet 1 INVENTOR. M4 6 E. CUM M4 ATTORNEY Nov. 3, 1953 M. E. CUSHMAN 2,657,755

VARIABLE PITCH PROPELLER Filed Aug. 28, 1947 5 Sheets-Sheet 2 F /Ja. 2

' ATTORNEY Nov. 3, 1953 u5 2,657,755

VARIABLE PITCH PROPELLER' Filed Aug. 28, 1947 5 Sheets-Sheet 5 BY %%7 h ATTORNEY Nov. 3, 1953 M. E. CUSHMAN 2,657,755

VARIABLE PITCH PROPELLER Filed Aug. 28, 1947 5 Sheets-Sheet 4 INVENTOR.

BY M W ATTORNEY Nov. 3, 1953 M. E. CUSHMAN 2,657,755

VARIABLE PITCH PRQPELLER Filed Aug. 28, 1947 5 sheets-sheet 5 ATTORNEY Patented Nov. 3, 1953 VARIABLE PITCH PROPELLER Maurice E. Cushman, Verona, N. J., assignor to Curtiss-Wright Corporation, a corporation of Delaware Application August 28, 1947, Serial No. 771,022

6 Claims.

This invention relates to aircraft propellers and is concerned particularly with improvements in hydraulically actuated propellers along with novel control systems therefor. The invention comprises certain improvements in the propeller disclosed in my co-pending application Serial No. 651,264, filed March 1, 1946, now Patent No. 2,640,555, and further is associated with propellers including compensated blade mountings to overcome the pitch flattening effect due to centrifugal force disclosed in my co-pending applications Serial Nos. 598,791 and 598,792, both filed June 11, 1945, now Patents 2,514,477 and 2,533,358, respectively, and Serial No. 722,253, filed January 15, 1947, now Patent No. 2,566,696.

Application Serial No. 651,264 discloses a propeller hub and blade pitch changing mechanism which includes an annular piston and cylinder assembly coaxial with the propeller shaft, wherein the external cylinder wall is stationary and the internal cylinder wall rotates with the propeller. With the stationary wall is associated a housing containing the hydraulic control system for the propeller and a speed sensitive governor. Propeller speed is controlled by changing blade pitch and hence, load on the prime mover, pitch change being initiated by the sensing of speed errors by the governor.

In the present invention, the pitch change mechanism and propeller hub is similar to that previously disclosed but, instead of the propeller incorporating its own speed responsive governor, it is provided with a blade angle control mechanism adapted to be associated with a separate control system, such as that of the power plant. Two blade pitch control arrangements are disclosed; one, called beta control, serving to adjust propeller pitch to a desired blade angle and the other, called rate control, serving to adjust the propeller mechanism to secure increased or decreased pitch at such rates of pitch change as may be called for by the separate control system.

Objects of the invention are: to provide a selfcontained hydraulically actuated propeller; to provide, in a propeller assembly, a non-rotating housing forming a part thereof which carries all of the mechanism essential to attain the desired range and/or rate of operation of the propeller; to provide a unitary propeller assembly, wherein the blades are changeable in pitch through a servomotor system and wherein a control is provided for external operation which may be moved to effect increased pitch, decreased pitch, feathering, and reverse pitch; to provide a pitch indicating system which will, at all times, indicate the actual pitch position of the propeller blades; to provide a hydraulic propeller system whose pitch change is effected through a servomotor system which secures pitch changing power from propeller rotation; to provide an accumulator system as part of the unit propeller assembly by which pitch changes may be effected when the propeller is not rotating, or is rotating at such a low speed as to provide inadequate power to effect pitch change; to provide a pumping system in a selfcontained hydraulic propeller wherein pressure levels in the propeller will be held at desired values for propeller operation and which will inhlbit leakage of hydraulic fluid from the propeller; to provide a fluid supply sump as part of a unit propeller assembly which is insensitive to position or acceleration and which thereby will furnish the propeller mechanism with adequate operating fluid in all attitudes and conditions of operation of the airplane with which the propeller is associated; to provide a propeller which is particularly adaptable for use with gas turbines as distinguished from reciprocating engine power plants; and to provide a propeller having variable rates of pitch change in accordance with demands made upon the propeller by the aircraft and power plant combination.

Further objects of the invention wil1 become apparent in reading the annexed detailed description in connection with the drawings. It is to be expressly understood, however, that the drawings and description are merely exemplary of one manner of accomplishing the teachings of the invention and the scope of the invention is only to be construed from the subjoined claims.

In the drawings, in which similar reference characters denote similar parts,

Fig. l is a side elevation of a unitary propeller assembly with the operating mechanism in longitudinal section;

Fig. 2 is a transverse section through the operating mechanism of the propeller substantially on the line 2--2 of Fig. 1;

Fig. 3 is a sectional plan of the portion of the propeller operating mechanism on the line 3-3 of Fig. 1; Figs. 4 and 5 are schematic diagrams of one embodiment of the propeller operating mechanism, pertaining to a rate type of pitch change control, Fig. 4 showing the system in normal operating condition and Fig. 5 showing the system in feather position; and

Fig. 6 is a schematic diagram of an alternative propeller operating system adapted for pitch angle or beta control, showing the system in the feathered blade position,

As stated, the invention includes two embodimentsa rate type of pitch change control and a pitch angle or beta type of pitch change control. The two systems are similar in most respects, and the differences between them will be pointed out in connection with a description of the schematic diagrams. The majority of the structural components of the propeller for both control arrangements are the same. Figs. 1, 2 and 3 includecontrol provisions applicable to the beta control.

Referring first to Figs. 1, 2 and 3, I provide a propeller hub l having blade sockets l2 (one being shown) from which extend propeller blades l4. The mounting of the blades in the hub sockets is preferably in accordance with the teachings of the previously mentioned applications although any appropriate type of blade mounting may be used. The hub I0 is mounted upon a propeller shaft [6 through splines [8, the system utilizing the conventional form of propeller hub nut, not shown, by which the propeller is secured on the shaft. The propeller hub l8 carries a rearward integral extension surrounding a portion of the propeller shaft and coaxial therewith and comprising an inner annular cylinder wall upon which an annular piston 22 is freely slidable. The piston 22 as well as the sleeve 28, closure 84 and rear partial closure elements secured to the cylinder 28, rotate with the propeller and the piston 22 is connected to the several propeller blades by rods 24 secured thereto and extending into the hub 18 for engagement with appropriate mechanism on the root ends of the propeller blades. Embracing the piston 22 is a stationary or non-rotating cylinder 26, non-rotatively secured to and within a housing 28 resiliently engaged with appropriate studs 38 springing from a power plant nose plate 32, the studs 38 serving to constrain the housing and its associated parts against rotation. The entire housing 28 and its contained and associated parts, however, is carried by and piloted on the propeller hub so that, while the housing does not rotate with the propeller, it is piloted on the propeller so that the propeller may rotate relative to it. The housing thus forms part of the propeller assembly and is removable with it as the propeller is removed from the shaft [6. On the left end of the cylinder assembly as shown in Fig. 1, a primary rotating seal 84 is indicated to minimize leakage from the leftward end of the annular cylinder and a rotating front closure 84 when the cylinder interior is exposed to fluid pressure. Fluid which may leak past the primary seal flows into a cavity 36 connected to a nonrotating sump at atmospheric pressure. Leakage from the cavity 38 is minimized by a secondary seal 38 between the rotating member 84 and the non-rotating housing elements, any leakage passing the seal 38 being caught in a labyrinth 40 in the non-rotating housing 28 whence it flows to a scavenger pump 42 (Fig. 2) and thence to a non-rotating sump 44 in the housing 28.

In somewhat the same fashion a primary seal 46 is arranged between the non-rotating cylinder 26 and a closure 41 secured to and rotated with the extension 28 toward the right hand end of the cylinder 26, such seal being backed up by a secondary seal 48, between rotating and nonrotating parts, the space between the seals being connected to the non-rotating sump 44 and the space downstream of the secondary seal 48 lead- '4 ing to a labyrinth 58 whence fluid bleed is scavenged by the pump 42 and returned to the sump 44.

Within the housing proper, the fluid sump 44, shown in section in Fig. 2, is contained, this sump including a filler opening 52 capped at 54 and leading to a plurality of passages such as 58, each opening into a different portion of the hydraulic system and one leading to the sump proper. The several filler passages 56 enable complete filling of the system when empty so that the hydraulic fluid does not have to be bled from the sump proper into the several portions of the system. The upper portion of the sump, occupying the upper portion of the housing 28, leads to left and right chambers 58 and 88 in the lower housing portion through passages 82 and restricted ports 64, the latter ports being disposed toward the bottom of the chambers 58 and 88 and the chambers being defined from the housing 44 by walls 66 integral withv the housing 28. The uppermost portions of the chambers 58 and 68 are vented as at 88 to the upper sump 44 through small restricted openings. Fluid in the upper sump 44 flows through the passages 62 and the ports 64 to fill the chambers 58 and 68, the air in these chambers venting into the upper sump through the openings 88. Fluid from the chambers 58 and 60 is led through openings 10 into an annular passage 12 surrounding the cylinder 20 which passage forms a manifold from which the pro peller mechanisms are supplied with fluid. In operation, the chambers 58 and remain filled at all times so long as the level of fluid in the entire sump system is adequate for operation. Should the housing be inverted for a reasonable interval, the chambers 58 and 60 will remain full of fluid to a suflicient extent to feed the hydraulic system, although that fluid in the upper sump 44 may flow away from the passages 62. Upon restoration of normal attitude, the fluid in the upper sump 44 will again be available to feed the chambers 58 and 88 and any minor fluid withdrawal from said chambers will be made up from the normal fluid supply.

The annular passage 12 and its associated hydraulic parts are at atmospheric pressure. The fluid in the passage 12 feeds the eye of the impeller of a centrifugal booster pump 14 which discharges into a passage 16 leading to the inlet of a positive gear pump 18. The gear pump discharge 88 is connected through ports shown in the schematic diagrams to furnish pressure fluid. to the annular cylinder in the propeller through the control mechanism to effect pitch change of the propeller. Working fluid in the system, after use in the propeller mechanism, is returned to the passage 16 so that there is no tendency to bleed the chambers 58 and 58 dry even when the aircraft attitude temporarily separates the chambers 58 and 60 from fluid communication with the upper supply sump 44.

The several pumps 42, 14 and 18 are housed in the stationary housing 28 and are driven as shown in Fig. 1, by a gear 82 integral with a back plate 84 secured to the propeller hub "I. Said gear 82 meshes with a pinion 88 forming a part of the impeller of the booster pump 14, the shaft of the latter being directly connected to one of the gears of the gear pump 18. The other gear of the gear pump carries a shaft 88 upon which is formed (as shown in Fig. 2) the impeller of the scavenger pump 42. The pump components of the assembly are contained within a sandwiched housing secured to a lower flat face of and forming a part of the housing 20, the elements of the lower housing comprising an upper member 90, an intermediate member 92 and a lower member 94. As will be clear in Fig. 2, these elements 90, 92 and 94 are so designed as to lie within the circular envelope defined by the stationary housing 28, the entire housing assembly having a diameter slightly greater than the circle defined by the outermost parts of the blade sockets I2 on the hub I0.

The housing elements 90, 92 and 94 further contain, or have attached thereto, components including valves and the like by which pitch change of the propeller is controlled. These components will be most clearly understood in connection with the description associated with the schematic views of Figs. 4, 5 and 6.

Disposed on substantially vertical axes along the side portions of the housing 20 is a pair of integral accumulator flasks 96, these flasks containing dry inert gas under pressure and serving, as will be described, to provide power for normal propeller pitch change, and for final feathering and initial unfeathering of the propeller when the latter is rotating slowly or not at all. The flask walls are integral with the housing 28 and each flask contains an elastic diaphragm 98 serving as a floating piston to isolate the pressurized gas from hydraulic fluid contained in the flask. The passages leading hydraulic fluid to and from the accumulator flasks which are connected to the tops of the accumulators, are shown functionally in the schematic views and have been omitted in Figs. 1, 2 and 3 to minimize complexity of these figures. The two accumulators are preloaded with inert gas at different pressures, for instance, 100 and 500 pounds per square inch. The low pressure flask provides comparatively large fluid capacity, for unfeathering, in the low pressure range, while the high pressure cylinder provides large fluid capacity in the high pressure range between the loading and unloading pressure settings of the pump unloading valve II2, to be described. The accumulators are parallel connected.

If hydraulic system pressure is in a low range between, say, 100 to 300 pounds per square inch, the low pressure flask will be partly full and will provide a substantial pressurized liquid supply for system operation, particularly for unfeather- 0 ing the propeller. At this low system pressure, the high pressure flask will be empty of liquid since the gas pressure therein is higher than low system pressure.

If system pressure is in a normally high operating range of, say, 500 to 700 pounds per square inch, the high pressure flask will be partly full and will provide a highly pressurized liquid supply in amount adequate for system operation for pitch change in normal operation and for feathering. At this high system pressure, the low pressure flask will be substantially full of liquid at high pressure but will remain relatively unavailable while system pressure remains high due to the small amount of gas in the flask.

Charging of the flasks with liquid occurs in sequence; as the pump operates, pressure builds up and fills the low pressure flask. Continued pump operation further builds up pressure in both flasks and fills the high pressure flask until pressure reaches a value to unload the pump. This arrangement enables the accommodation of a large amount of liquid for system operation in the high pressure region, the liquid being predominantly in the high pressure flask which has a large amount of gas therein. The fairly large amount of liquid for use in the low pressure region remains in the low pressure flask which has a small amount of gas therein. Inherently, the supply of liquid available between the high and low regions will be small, but much liquid is not needed in the intermediate region. Thus, an economy of material and bulk is secured by the two-flask arrangement. When liquid is withdrawn in high pressure operation, the majority of it comes from the high pressure flask, and a small amount only from the low pressure flask.

The arrangement may be compared to two compression springs in series, one a soft spring and the other a stiff spring. Initial force on the soft spring compresses it until it reaches solidity, and a large increment of force is then needed to compress the stiff spring. Upon expansion, the stiff spring provides considerable force over a substantial distance until it has extended; then the soft spring exerts its force over a further range of distance.

Reference is now made to Figs. 4 and 5 which show the hydraulic systems in schematic fashion, those components of the system which have al ready been described bearing the same reference characters as in Figs. 1, 2 and 3.

In this arrangement a control level I00 operable manually or preferably by a coordinated control mechanism exteriorly of the propeller is effective to change the rate or pitch change of the propeller either in a pitch increasing or a pitch decreasing direction. The lever I00 is normally disposed adjacent a portion of the stationary propeller housing '20, 90, and is mounted on a shaft which carries a pinion I02 engaging a rack rod I04 upon the leftward end of which is a control valve I06. This valve is also shown in Fig. 3. The valve is disposed in a bore I08 (in the housing to which a plurality of passages are connected. One of these passages IIO supplies pressure fluid to the valve bore and leads thereto from an unloading valve assembly I I2 and from an accumulator valve assembly H4. The unloading valve assembly, known in the art and described in detail in my co-pending application Serial No. 651,264, is provided with pressure fluid on demand from the gear pump I8 through the conduit 80. The accumulator shut-off valve II4 when open, connects the accumulators with the passage I I0 and the unloading valve assembly I I2. The accumulator shut-off valve is automatic in its operation and is that type of valve which is disclosed in my co-pending application Serial No. 743,748 filed April 25, 1947, now Patent No. 2,556,719.

' The valve bore I00 has a port and associated passage IIB leading to the leftward end of the propeller annular cylinder 26, said valve bore having another port and passage II8 leading therefrom to the right hand end of the propeller annular cylinder. The outer ends of the valve bore are provided with ports and passages I20 connected on the one hand to a control portion of the accumulator shut-off valve I I4 and on the other hand to the delivery side of the booster pump 14 and to the intake side of the gear pump I8 as at I6. When the valve I06 is moved to the right, as shown in Fig. 4, pressure fluid is admitted through the passage IIO, the valve I06 and the passage I I8 to the right hand end of the annular piston, urging pitch increase. Fluid in the left end of the annular cylinder is returned through the passage IIS and the valve I06 to the gear pump intake Hi. When the valve I06 assay.

is moved leftwardly, the port H is connected with the port H6 whereby pressure fluid passes to the left end of the propeller annular cylinder to cause pitch decrease of the propeller blades. As pitch of the blade decreases, fluid at the right hand end of the annular cylinder 26 is discharged through the passage H8 and the valve I06 to the pasage I6 for recirculation in the pump systemf The rate of change of pitch is established by the degree to which the ports H6 and H8 are opened.

The turbine control or other control mechanism operating the valve lever I00 and valve I06 is so arranged as to call for pitch increase or pitch decrease at varying rates of pitch change and furtheris so arranged as to shut off the ports H6 and H8 when no pitch change is needed, thus providing a hydraulic lock. The control system operating on the lever I00 likewise is controllable to call for reverse pitch operation of the propeller and for feathering movement of the propeller. For reverse pitch, a pitch decrease is demanded and is carried to the point where the blade I4 rotates until reverse pitch positioning of the blade is attained. When feathering is called for, the mechanism operating on the lever I00 calls for feather and increased pitch as shown in Fig. 5 and remains in that position throughout feathered operation of the propeller.

Since the operation of the pump system of the propeller depends upon propeller rotation, a propeller pitch position will be reached during feathering where propeller rotation is low and where insufficient capacity may be available from the pump I8 to accomplish, without aid by the accumulators 96, the final phases of feathering. To this end, the accumulators 9 6 automatically provide the necessary power for final feathering, these accumulators having been charged during normal operation and having suflicient capacity not only to accomplish final feathering of the propeller but to accomplish unfeathering of the propeller when such a demand is made after the propeller has been feathered. After complete feathering, the accumulator shut-off valve H4 closes the pressure line H0 serving the control valve I06, from the accumulator conduit I24, whereby the accumulators are isolated from the system during inactivity of the propeller. Upon call for decrease in pitch after feathering, the accumulator shut oif valve H4 is opened concurrently with a decrease pitch demand in the valve I06 whereby accumulator pressure passes through the lines I24 and H0 to the valve bore I08 whence the fluid pressure passes to the port and passage H6 to initiate pitch decrease. As propeller rotation starts due to windmilling action, the pump system begins to operate to provide pressure fluid necessary to recharge the accumulators, and, possibly brin propeller pitch to a normal operating level. The valve H4 remains open during normal or reverse pitch operation.

The accumulators, during normal operation, are held at a pressure level between high and low limits, and provide the power needed for normal propeller pitch increase and decrease. When the pressure level in the accumulators drops to the low limit, established by the setting of the unloader valve unit H2, the pump I8 is loaded and replenishes the accumulators to the high pressure limit. The unloader valve I I2 loads and connects the pump I6 to the passage I II! when accumulator pressure is low and unloads and disconnects the pump I8 from the accumulator system th Passages HQ nd I? when h amma: later ressu e has se to the hi h pressure s wil b s n from the schem tic d a ram. he nes betwe n prima and seco da S als. It 38 a .6. 4a in he annu r Pr p ller nd r are c ect d h ou h a. passa e '25 t9 the su p 44. T y m 44 ma ntained a atm s h ic P u by ven in it rou h t e ine to e impel r e e o he a en e u p 431,538! impeller having vent holes I29 therethrough to connect the vent with the Scavenger pump'inlet line leading from the labyrinths and 50, Fluid n t la r nth fl b ra i y to h p m 2. which acts as a flui -a r eparator d i ries fluid to the sump but allowing air flow in either direction for venting the sump 44. The scaven ger pump further Pre ents o s of f ui rom, t e sump when the airplane may be inverted, by pumping fluid through a vent line I26a back to the sump. ,Sump fluid may pass from the sump chambers 58 and 60 through the channel I2 and a passage I30 to the intalge of the booster "I4, the output of the latter pump charging the intake of the gear pump I8 and likewise main: taining a booster pressure, substantially less than the pressure delivered by the gear pump I6 or the accumulators 85, in hat nd of the pro peller annular cylinder which is not being pressure fluid loaded by a call for pitch change, this connection being established through the ports and passages I20 from the bOQStGfDllIllD, dis! charge I6. I 1

When the unloader valve I I2 unloads the gear pump I8, the gear pump discharge, at low pres? sure, is directed through a passage I3I leading to a filter I32 and thence to the sump chambers 56 and 60 through the passage I2.

Positive indication of the pitch of the propeller blades is at all times available through the medium of a shoe I34 bearing on the propeller annular piston 22 and connecting through a flexible strip I36 to a bevel gear set I38 associated with the cylinder wall 26, the driven gear of said gear set carrying a pinion or sector I40 engaged with a rack formed on a rod I42. Some of these elements are shown in Flgs. 1, 2 and 3 whereby their location in the propeller assembly is made clear. The rod I42 is translated to left and right in accordance with the actual pitch position of the propeller blades andis urged as shown in Fig. 4 in a leftward direction by a small piston-cylinder unit I44 which is fed from the accumulator conduit I24 so that the shoe I34 is at all times urged into contact with the an nular piston 22. A rightward extension of the rod I42 carries a rack I 46 engaged with a pinion I48 to which an arm I50 may be secured, said arm projecting from a portion of the propeller hous ng assembly for connection to pitch indication pickup devices in the propeller control system. Where a rate type of propeller pitch control is utilized in conjunction with a gas turbine, the control system normally requires a pitch signal for its coordinated operation in adqustment of propeller blade pitch. The pitch nd cating arm I50 provides such a signal. I

At the right hand end of Fig. 4 is show n a cross l nk I52 loosely engaging elongated slots in the right hand ends of the rack rod I42 and the valve actuating o 04. At its upper end, the link I52 is hinged to a sliding member I54 as at I 55, said member being engageable at times with a rocker arm I56 pivoted to fixed structure at I60, the other end of said arm being engageable w th a rod I62 forming a elf the accumulator shut-01f valve system II4. Under all conditions except when the propeller is at or near feathering, the rod N32 is pressed leftwardly by a spring I64 whereby the accumulator shut-off valve H4 is constrained toward the open position as shown in Fig. 4.

When the control arm I is moved to the extreme left position as shown in Fig. 5., calling for feathering, the lower end of the link I52 is moved to the right by the rod I04. As the propeller pitch increases, the pitch indicator rod I42 moves leftwardly and prior to final feathering, through the member I54, rocks the arm I58 counter-clockwise as shown in Fig. 5, relieving the accumulator shut-off valve rod I62 of the spring pressure normally tending to hold it in a leftward position. When propeller feathering is finally completed, as when the piston 22 reaches the limit of its stroke, the accumulator shut-ofi valve II4 closes by the change in pressure relationships occurring when the system becomes inactive, in which position it remains while the propeller is feathered.

Upon a call for unfeathering, the control valve rod I04 is moved leftwardly thereby freeing the lower end of the link I52, the upper link end then moving to the right around the pivot of the rod I45 and unloading the rocker arm I58. The spring I04 then forces the accumulator shutoff valve control rod I62 to move to the left, which adjusts the pressure relationships in the shut-off valve II4 so that the latter opens, connecting the accumulator to the propeller to effect pitch decrease. As the pitch decrease continues, the propeller windmills, pump pressure can be built up in the system and the accumulators become recharged to operate in conjunction with the pump as previously described.

Reference should now be had to Fig. 6 which shows the propeller system adapted for beta control or pitch position control. The entire system is substantially identical with that previously described save for the right hand end of the schematic systems depicted. The sliding member I54 in this arrangement is provided with rack teeth engaged by a pinion sector I10 actuated by an appropriate control or arm I12. The rack member I54 serves the same purpose with respect to the accumulator shut-ofi valve and the rocker arm I58 as it did in the previously described embodiment. However, the member I54 serves the further purpose of establishing finite pitch positions of the propeller. A link I14 is pivoted at I56 to the sliding member I54 and is likewise pivoted as at I16 to the pitch indicator rod H2 and at I18 to the control valve rod 504. These elements are also shown in Fig. 3. When the sliding member I54 is moved to some new position from a previous position, say to the right, the link I14 will be swung clockwise about the pivot I16 as a center, moving the control valve rod I04 to the left thereby calling for pitch decrease. When the pitch decreases, the indicator rod I42 moves toward the right causing the link I14 to swing counter-clockwise about the pivot I56 whereby'the valve control rod I04 is restored to a central position calling for no pitch change, as the preset pitch value has been attained. This in effect becomes a servo followup system so that any pitch position demands dictated by movement of the control arm I12 initiate pitch change at a rate which gradually becomes less as propeller pitch position approaches the desired value, finally cutting off connected to said blades and including amot or,

a pressure source, a

said motor, "a supply conduit to said pressure vides a graduated type of control wherein initiation of pitch change in small amounts causes movement of the blades in pitch at a low rate, and wherein initiation of pitch change demands of large amount calls for high rate of pitch change at the beginning which gradually becomes less as the pitch approaches the desired value.

The basic structure of the propeller herein described remains the same for both the rate and beta type of controls, the only essential change residing in substitution of one type of control linkage for the other. The propeller structure has been designed to permit comparatively simple change from one system to the other, the essential changes involving the substitution of the links 514 and I52 and associated control elements. These changes may readily be made by removing the auxiliary housing I80 (Figs. 2 and 3) which covers the link system, and substituting one set of link and associated parts for the other. In the case of the rate control propeller (Figs. 4 and 5), the rate control element I00 would be borne in the housing I80 and would carry a pinion engaging a rack extension of the control valve stem I04.

The unloader valve assembly II2 shown in the schematic View is disposed in an auxiliary housing, bearing the same number, secured to the right hand end of the lower attached housing portions shown in Fig. 2. The accumulator shutoff valve assembly II4 shown in the schematics is disposed in a cavity bearing the same reference character within the housing 90. Other associated parts of the control system, where it is feasible to do so without unduly complicating Figs. 1, 2 and 3, are shown and numbered with the same characters which are used for them in the schematic diagrams. It will be appreciated that the housing elements such as 28, 90, 92 and 94 may be cored and drilled to provide the various fluid passages shown in the schematic drawings, in all instances said passages being short and direct between the members and components which they connect. It is considered that the disposition and location of passages of the type described comes within the scope of those skilled in the art, and accordingly, a detailed showing of these passages has not been rendered in the drawings.

Though several embodiments illustrating the invention have been shown and described, it is to be understood that the invention may be applied in other and various forms. Changes may be made in the arrangements, without departing from the spirit of the invention. Reference should be had to the appended claims for definitions of the limits of the invention. I

What is claimed is:

1. In a controllable pitch propeller comprising a rotatable hub having blades mounted therein for pitch change and a non-rotating housing ournalled on the hub, said housing containing a hydraulic pitch change mechanism operably feed conduit therefrom v to source, a discharge fluid conduit receiving fluid from said motor, a scavenging conduit connected in said mechanism to receive leakage and surplus fluid, and a fluid sump comprising two chambers normally superimposed and in restricted communication with one another, said supply and pitch hange a the value is reached. This prodischarge conduits being connected to the lowera 1i moatchamhenand, aid;sceveng1ng eqnduit being oonnectedfito, the. uppermqst chamber n V 'zhlnwatcontrollable pitch-propeller cqm rismg i rotatable, ,huh; having blades vlmnl l ed wtherein tar pitch. ch nge and a,.non:1-o. a Mus ng 'joumalled; on. th.e nub, said hou in c n a n n a hydraulic pitch change mechanism opfi fflbl mnnected. pfisai des 4 nd includin a m t ammsu e. o rce, vae ee d VQ n ui th re r m Y to wd m qxma .supply e ,cpnd t sa pre su source. xvii h e fluidecon t .rece v ne flu d iron; said mqtor a, geavengingpopduitponnected maa d m chanism execeive leaka e an ur l fluid. hand .a. .fl id .sump, c m risi o. ammhno ma y. u er mnq edwand n.v rfi wd cnmmunicatign. wi h ed ne said p y an iqiw rse m uits ein nec to t m mellx l ermost e mb rend sa i yen il snnn mt bein conn tedi o h nq l pshame; s id ump ,iqrmins Pa t 9 s1 hou in JflQiPfiP i no rm et ble whereby 3431 92999 11?! .e ti de ,.the said n rmel yl w rp dsig sprgmphembey receives and dischafges fluid r P o l p rati n: 1

3. In a controllable piteh j1 )f epeiler,fe fireipels rm iedil dwl i szk ii epfi e zl to me g beei w piwh lm' p rt'bls e Seed .e-pi wneele wete daa sa l d m m; w thi whi h, wi mi 9z e em nt i HWY? v a a q nrt e e "nwi r ied b a d fit iz 'l' fe b e i l Said. L mo'tqn. and r i fi e d e e i e epq nt .11 S e ed m'v 3, li fit n. t wfl fe elemet he t et r n w (t b e-wit h Pr we-R fi w esi. 9

fi ish e-.q esaid. e em nts i eculed for ment, a secgndary seal between 5 fifp'aift' afid a.

driven bythe: prd' ene; 'inchidi ri g 'a, high 'bi'es'silge "pm-p dehyerin'g' Operating fluid toithemetorfaxid *a. low pressure pump fed from Said'sump and 

